Intel on its website has published a page on the Z390 chipset, including a chipset block diagram showing all connections. Z390 will support all  Coffee Lake generation desktop processors but would also be compatible for the next-generation. 

Z390 has been discussed a lot, it should be a chipset intended for 8-core Coffee Lake CPUs, but these are not expected to launch anytime soon. Z390 will get an LGA1151 socket using the traditional DMI 3.0 chipset-bus (which basically is an x4 PCIe link lane up/downlink. Similar to the Z370 chipset, it'll have 24 PCI-Express gen 3.0 lanes. Also similar is storage at six SATA 6 Gbps ports with AHCI and RAID support; and up to three 32 Gbps M.2/U.2 connectors. LAN remains the same as well. 1 GbE, Intel recommends their Wireless-AC 9560 card for the motherboard manufacturers to pair this chipset with for 802.11ac and Bluetooth 5. Some differences are spotted though, USB is configured at six 10 Gbps USB 3.1 gen 2 ports, ten 5 Gbps USB 3.1 gen 1 ports.

All in all, there are very little changes, other than new CPU support. You can find more info here.

Above Intel Z390

Above (for comparison) Z370